The Distribution of Senescence 



In comparative studies of animal senescence we have three 

 main types of information: single records of the extreme re- 

 corded longevity of different species under various conditions; 

 observations on the composition of natural populations, 1 and 

 marking experiments, which give a measure of longevity and 

 mortality under natural conditions; and life- tables and com- 

 parable material plotted for animals under domestic and labor- 

 atory conditions, which indicate the susceptibility of these 

 species to eventual senescence, either by measuring the force of 

 mortality, or by measuring subsidiary age-characters such as 

 reproductive capacity. Studies of senescence in domestic animals 

 are singularly deficient, since apart from individual pets of 

 various phyla neither farmers nor laboratories are usually inter- 

 ested in maintaining their stocks throughout the whole life- 

 cycle and on into senescence. While there are extensive data on 

 the early development of almost all animals of economic im- 

 portance, the senile period is a virtually unworked biometric 

 field. The literature does not even contain life-tables for repre- 

 sentative species of each class of vertebrate. There is only one 

 published life- table for birds in captivity (domestic fowls — 

 Gardner and Hurst, 1933) and that is incomplete. No life-table 

 appears to have been published for any reptile or fish, including 

 common and short-lived aquarium species, or even for dogs or 

 cats. Apart from man, adequate or partially adequate actuarial 

 data exist in the literature for the following animals in captivity: 



Mice (KoboziefT, 1931; Murray and Hoffman, 1941; Grune- 



berg, 1951, etc.) (Fig. 31). 

 Rats (Slonaker, 1912; Wiesner and Sheard, 1934). 

 Rattus natalensis (Oliff, 1953). 

 Voles (Leslie and Ranson, 1940) (Fig. 30). 

 Sheep (partial) (Kelley, 1939). 

 Fowls (Gardner and Hurst, 1933). 

 Limnaea (Gastropoda) (Winsor and Winsor, 1935; Baily, 



1931) (Fig. 28). 

 Agriolimax (Gastropoda ) (Pearl and Miner, 1935) (Fig. 5c). 



1 Methods of age determination in fish, molluscs and mammals have been 

 well reviewed (Trans. N.T. Acad. Scl, 16, no. 6, 1954) and their value 

 criticized. 



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